Chapter 10 Earthlike Planets: Venus and Mars
10.9 Questions and Exercises
Review Questions
1: List several ways that Venus, Earth, and Mars are similar, and several ways they are different.
2: Compare the current atmospheres of Earth, Venus, and Mars in terms of composition, thickness (and pressure at the surface), and the greenhouse effect.
3: How might Venus’ atmosphere have evolved to its present state through a runaway greenhouse effect?
4: Describe the current atmosphere on Mars. What evidence suggests that it must have been different in the past?
5: Explain the runaway refrigerator effect and the role it may have played in the evolution of Mars.
6: What evidence do we have that there was running (liquid) water on Mars in the past? What evidence is there for water coming out of the ground even today?
7: What evidence is there that Venus was volcanically active about 300–600 million years ago?
8: Why is Mars red?
9: What is the composition of clouds on Mars?
10: What is the composition of the polar caps on Mars?
11: Describe two anomalous features of the rotation of Venus and what might account for them.
12: How was the Mars Odyssey spacecraft able to detect water on Mars without landing on it?
Thought Questions
13: What are the advantages of using radar imaging rather than ordinary cameras to study the topography of Venus? What are the relative advantages of these two approaches to mapping Earth or Mars?
14: Venus and Earth are nearly the same size and distance from the Sun. What are the main differences in the geology of the two planets? What might be some of the reasons for these differences?
15: Why is there so much more carbon dioxide in the atmosphere of Venus than in that of Earth? Why so much more carbon dioxide than on Mars?
16: If the Viking missions were such a rich source of information about Mars, why have we sent the Pathfinder, Global Surveyor, and other more recent spacecraft to Mars? Make a list of questions about Mars that still puzzle astronomers.
17: Compare Mars with Mercury and the Moon in terms of overall properties. What are the main similarities and differences?
18: Contrast the mountains on Mars and Venus with those on Earth and the Moon.
19: We believe that all of the terrestrial planets had similar histories when it comes to impacts from space. Explain how this idea can be used to date the formation of the martian highlands, the martian basins, and the Tharsis volcanoes. How certain are the ages derived for these features (in other words, how do we check the ages we derive from this method)?
20: Is it likely that life ever existed on either Venus or Mars? Justify your answer in each case.
21: Suppose that, decades from now, NASA is considering sending astronauts to Mars and Venus. In each case, describe what kind of protective gear they would have to carry, and what their chances for survival would be if their spacesuits ruptured.
22: We believe that Venus, Earth, and Mars all started with a significant supply of water. Explain where that water is now for each planet.
23: One source of information about Mars has been the analysis of meteorites from Mars. Since no samples from Mars have ever been returned to Earth from any of the missions we sent there, how do we know these meteorites are from Mars? What information have they revealed about Mars?
24: The runaway greenhouse effect and its inverse, the runaway refrigerator effect, have led to harsh, uninhabitable conditions on Venus and Mars. Does the greenhouse effect always cause climate changes leading to loss of water and life? Give a reason for your answer.
25: In what way is the high surface temperature of Venus relevant to concerns about global warming on Earth today?
26: What is a dust devil? Would you expect to feel more of a breeze from a dust devil on Mars or on Earth? Explain.
27: Near the martian equator, temperatures at the same spot can vary from an average of –135 °C at night to an average of 30 °C during the day. How can you explain such a wide difference in temperature compared to that on Earth?
Figuring for Yourself
28: Estimate the amount of water there could be in a global (planet-wide) region of subsurface permafrost on Mars (do the calculations for two permafrost thicknesses, 1 and 10 km, and a concentration of ice in the permafrost of 10% by volume). Compare the two results you get with the amount of water in Earth’s oceans calculated in Example 10.1.
29: At its nearest, Venus comes within about 41 million km of Earth. How distant is it at its farthest?
30: If you weigh 150 lbs. on the surface of Earth, how much would you weigh on Venus? On Mars?
31: Calculate the relative land area—that is, the amount of the surface not covered by liquids—of Earth, the Moon, Venus, and Mars. (Assume that 70% of Earth is covered with water.)
32: The closest approach distance between Mars and Earth is about 56 million km. Assume you can travel in a spaceship at 58,000 km/h, which is the speed achieved by the New Horizons space probe that went to Pluto and is the fastest speed so far of any space vehicle launched from Earth. How long would it take to get to Mars at the time of closest approach?
